a) Field of the Invention
The present invention relates to an apparatus and method for lifting and removing larger and heavier objects which are at least moderately awkward to handle, and more particularly to such an apparatus and method for lifting and removing manhole covers from a manhole frame, and accomplishing this in a manner to facilitate the process to avoid injury to workers.
b) Background Art
Manholes are commonly located at streets and other surface locations to provide access to some underground location, and these are commonly used in connection with utilities (power or communication lines, sewers, etc.). When a workman travels to a site where some operation has to be for the utility, sewer, or other need, there is generally the preliminary task of removing the manhole cover, from the surface opening, and then replacing it.
There are various ways of accomplishing this, sometimes a crowbar-like tool is used to lift one edge of the manhole cover, after which a lever-like tool is used to lift it first vertically so that it is clear of the surrounding frame and then laterally.
The task of replacing the manhole cover is accomplished in somewhat the same manner.
Statistically, the task of removing and replacing manhole covers has been found to be a high risk operation in terms of promoting and or causing back and other muscular-skeletal injuries. In spite of this, to the best knowledge of the applicant herein, there has not as yet been devised a method and/or apparatus for removing manhole covers which has gained wide commercial acceptance, where the apparatus and/or method is effective and convenient, while providing little or substantially no risk of injury to the workers.
A search of the patent literature has disclosed a number of U.S. patents that deal with the problem of lifting manhole covers and the like, these are the following:
U.S. Pat. No. 4,181,290 (Affolter) shows a device for lifting a manhole cover or other vault cover. There is a base comprising three legs extending outwardly from a center location. There is an upright post, and a lifting arm is connected to the center base portion of the three legs and also is connected to the post. This arm is raised to lift the cover.
U.S. Pat. No. 4,488,706 (Kono) shows a manhole cover lifting device where there is a lever bar having a hook on the lifting end, and a rearwardly positioned handle. The bar is supported by a pair of wheels at the lifting location. The hook end of the bar is secured to the cover, and the opposite end of the bar is pushed downwardly to lift the manhole cover, as the bar pivots on the wheels which serve as a faucrum.
U.S. Pat. No. 4,365,925 (Gritz) shows a manhole cover lifter which is similar to the above mentioned Kona patent. There is a bar 11 that is supported by a set of wheels. One end of the bar is secured to the cover, and the other has a handle which is pressed downwardly to lift the manhole cover as the bar pivots on the wheels which serve as a faucrum.
U.S. Pat. No. 4,321,003 (Cassel) shows what is called a “lifting tool” and shows an arrangement in which a pair of anti-friction bearings, as shown in sheet 4 of the drawings of the patent, are secured to a elongate lift rod that clamps at each end to the vault cover. A handle is lifted to rotate the rod which is connected to the inner races of the bearings. These are rotated 180° so that the cover is raised high enough to be rolled on the outer races of the bearings.
U.S. Pat. No. 4,746,098 (Abarotin) shows a manhole cover lifting device in which there is a bar that extends from a ground supported pivot 17 to a handle at the other end. There is a means to attach the cover to the bar aligned on the center of the bar. In use the bar is secured to the cover and the handle end is lifted. The parts are pivoted on the member 17 so that the cover is swung out of the way.
U.S. Pat. No. 4,653,728 (Mochizuki) shows a manhole cover lifter where there is a pair of wheels, each of which is fastened adjacent to a grasping means. There are series of lever associated with the wheel mounts that enable the lifting and maneuvering of the lid.
U.S. Pat. No. 4,662,607 (Mochizuki et al) shows a lifting device where there is an elongate bar mounted to ground wheels at a location near the manhole the bar is used as a lever, with the wheels acting as a fulcrum to lift the manhole cover by the front portion of the bar.
U.S. Pat. No. 1,890,765 (Zent) shows an amusement park ride which in FIG. 17 is shown as a car with wheels mounted at angles to each other.